Elucidation of the mechanism of mitochondrial iron loading in Friedreich's ataxia by analysis of a mouse mutant

We used the muscle creatine kinase (MCK) conditional frataxin knockout mouse to elucidate how frataxin deficiency alters iron metabolism. This is of significance because frataxin deficiency leads to Friedreich''s ataxia, a disease marked by neurologic and cardiologic degeneration. Using cardiac tissues, we demonstrate that frataxin deficiency leads to down-regulation of key molecules involved in 3 mitochondrial utilization pathways: iron-sulfur cluster (ISC) synthesis (iron-sulfur cluster scaffold protein1/2 and the cysteine desulferase Nfs1), mitochondrial iron storage (mitochondrial ferritin), and heme synthesis (5-aminolevulinate dehydratase, coproporphyrinogen oxidase, hydroxymethylbilane synthase, uroporphyrinogen III synthase, and ferrochelatase). This marked decrease in mitochondrial iron utilization and resultant reduced release of heme and ISC from the mitochondrion could contribute to the excessive mitochondrial iron observed. This effect is compounded by increased iron availability for mitochondrial uptake through (i) transferrin receptor1 up-regulation, increasing iron uptake from transferrin; (ii) decreased ferroportin1 expression, limiting iron export; (iii) increased expression of the heme catabolism enzyme heme oxygenase1 and down-regulation of ferritin-H and -L, both likely leading to increased “free iron” for mitochondrial uptake; and (iv) increased expression of the mammalian exocyst protein Sec15l1 and the mitochondrial iron importer mitoferrin-2 (Mfrn2), which facilitate cellular iron uptake and mitochondrial iron influx, respectively. Our results enable the construction of a model explaining the cytosolic iron deficiency and mitochondrial iron loading in the absence of frataxin, which is important for understanding the pathogenesis of Friedreich''s ataxia.     

Murrayafoline A Induces a G0/G1-Phase Arrest in Platelet-Derived Growth Factor-Stimulated Vascular Smooth Muscle Cells

The increased potential for vascular smooth muscle cell (VSMC) growth is a key abnormality in the development of atherosclerosis and post-angioplasty restenosis. Abnormally high activity of platelet-derived growth factor (PDGF) is believed to play a central role in the etiology of these pathophysiological situations. Here, we investigated the anti-proliferative effects and possible mechanism(s) of murrayafoline A, a carbazole alkaloid isolated from Glycosmis stenocarpa Guillamin (Rutaceae), on PDGF-BB-stimulated VSMCs. Murrayafoline A inhibited the PDGF-BB-stimulated proliferation of VSMCs in a concentration-dependent manner, as measured using a non-radioactive colorimetric WST-1 assay and direct cell counting. Furthermore, murrayafoline A suppressed the PDGF-BB-stimulated progression through G₀/G₁ to S phase of the cell cycle, as measured by [³H]-thymidine incorporation assay and cell cycle progression analysis. This anti-proliferative action of murrayafoline A, arresting cell cycle progression at G₀/G₁ phase in PDGF-BB-stimulated VSMCs, was mediated via down-regulation of the expression of cyclin D1, cyclin E, cyclin-dependent kinase (CDK)2, CDK4, and proliferating cell nuclear antigen (PCNA), and the phosphorylation of retinoblastoma protein (pRb). These results indicate that murrayafoline A may be useful in preventing the progression of vascular complications such as restenosis after percutaneous transluminal coronary angioplasty and atherosclerosis.     

Virus Detection and Semiquantitation in Explanted Heart Tissues of Idiopathic Dilated Cardiomyopathy Adult Patients by Use of PCR Coupled with Mass Spectrometry Analysis

Viral detection in heart tissues has become a central issue for the diagnosis and exploration of the pathogenesis of idiopathic dilated cardiomyopathy (IDCM). In the present study, common cardiotropic viruses in 67 explanted heart samples of 31 IDCM adult patients were detected and semiquantified by using for the first time a new technology based on PCR assay coupled to electrospray ionization-time of flight mass spectrometry analysis (PCR-MS), with comparison to reference quantitative real-time PCR (RT-qPCR) assay. PCR-MS identified single or mixed enterovirus (EV) and parvovirus B19 (PVB19) infections in 27 (40.2%) of 67 samples, corresponding to 15 (48.3%) of the 31 patients, whereas RT-qPCR identified viral infections in 26 (38.8%) samples, corresponding to 16 (51.6%) of the patients. The PCR-MS results correlated well with EV and PVB19 detection by RT-qPCR (kappa = 0.85 [95% confidence interval {CI}, 0.72 to 1.00] and kappa = 0.82 [95% CI, 0.66 to 0.99], respectively). The levels of EV RNA (median, 550 [range, 178 to 3,200] copies/μg of total extracted nucleic acids) and of PVB19 DNA (median, 486 [range, 80 to 1,157] copies/μg of total extracted nucleic acids) were measured using PCR-MS and correlated with those obtained by RT-qPCR (r² = 0.57, P = 0.002 and r² = 0.64, P < 0.001 for EV and PVB19, respectively). No viruses other than EV and PVB19 strains were detected using the new PCR-MS technology, which is capable of simultaneously identifying 84 known human viruses in one assay. In conclusion, we identified single or mixed EV and PVB19 cardiac infections as potential causes of IDCM. The PCR-MS analysis appeared to be a valuable tool to rapidly detect and semiquantify common viruses in cardiac tissues and may be of major interest to better understand the role of viruses in unexplained cardiomyopathies.     

Frequent occurrence of parvovirus B19 DNAemia in the first year after kidney transplantation

Described for the first time in 1986, Parvovirus B19 (B19V) infection in kidney transplant recipients remains little‐known and probably underestimated. The aims of this study were to establish B19V infection frequency during the first year after kidney transplant and to determine predisposing factors and manifestations of the infection in renal transplant recipients. Sixty consecutive adult patients, transplanted less than a year before, were included in this study. B19V and other opportunistic viral infections were detected retrospectively in plasma samples collected every 15 days during the first 3 months and every month from 3 months to 1 year following the kidney transplant. Demographic characteristics, immunosuppressive treatment and biological findings were recorded on each sampling date. Six patients (10%) presented B19V viremia, while eight CMV (13.3%), seven EBV (11.7%), five HHV‐6 (8.3%), five BKV (8.3%), and two adenovirus (3.3%) infections were detected. The mean value of B19V viral load was 149 UI/ml. B19V infections were either reactivation or reinfection due to genotype two in five cases, while one case of primary infection with genotype 1 was observed. Neither risk factors nor biological consequences of B19V infection have been identified. These results rank B19V third among opportunistic viral infections occurring during the first year after a kidney transplant. With regard to this high incidence, and even if the risk factors and biological consequences of the infection should be assessed in larger studies, the question of systematic screening and follow‐up of B19V infection in kidney transplant recipients is relevant. J. Med. Virol. 85: 1115–1121, 2013. © 2013 Wiley Periodicals, Inc.     

Suture button suspension following trapeziectomy in a cadaver model

Background

The safety and the effects of different trajectories on thumb motion of suture-button suspensionplasty post-trapeziectomy are not known.

Methods

In a cadaveric model, thumb range of motion, trapeziectomy space height, and distance between the device and nerve to the first dorsal interosseous muscle (first DI) were measured for proximal and distal trajectory groups. Proximal trajectory was defined as a suture button angle directed from the thumb metacarpal to the second metacarpal at a trajectory less than 60° from the horizontal; distal trajectory was defined as a suture button angle directed from the thumb metacarpal to the second metacarpal at a trajectory of greater than 60° from the horizontal (Fig. 1).

Results

There were no significant differences in range of motion and trapeziectomy space height between both groups. The device was significantly further away from the nerve to the first DI in the proximal trajectory group compared to the distal trajectory group, but was still safely away from the nerve in both groups (greater than 1 cm).

Conclusions

These results suggest that the device placement in either a proximal or distal location on the second metacarpal will yield similar results regarding safety and thumb range of motion.     

Controlling posture using a plantar pressure-based,tongue-placed tactile biofeedback system

The present paper introduces an original biofeedback system for improving human balance control, whose underlying principle consists in providing additional sensory information related to foot sole pressure distribution to the user through a tongue-placed tactile output device. To assess the effect of this biofeedback system on postural control during quiet standing, ten young healthy adults were asked to stand as immobile as possible with their eyes closed in two conditions of No-biofeedback and Biofeedback. Centre of foot pressure (CoP) displacements were recorded using a force platform. Results showed reduced CoP displacements in the Biofeedback relative to the No-biofeedback condition. The present findings evidenced the ability of the central nervous system to efficiently integrate an artificial plantar-based, tongue-placed tactile biofeedback for controlling control posture during quiet standing.     

How a plantar pressure-based,tongue-placed tactile biofeedback modifies postural control mechanisms during quiet standing

The purpose of the present study was to determine the effects of a plantar pressure-based, tongue-placed tactile biofeedback on postural control mechanisms during quiet standing. To this aim, 16 young healthy adults were asked to stand as immobile as possible with their eyes closed in two conditions of No-biofeedback and Biofeedback. Centre of foot pressure (CoP) displacements, recorded using a force platform, were used to compute the horizontal displacements of the vertical projection of the centre of gravity (CoG _v ) and those of the difference between the CoP and the vertical projection of the CoG (CoP-CoG _v ). Analysis of the CoP-CoG _v displacements showed larger root mean square (RMS) and mean power frequencies (MPF) in the Biofeedback than in the No-biofeedback condition. Stabilogram-diffusion analysis further showed a concomitant increased spatial and reduced temporal transition point co-ordinates at which the corrective processes were initiated and an increased persistent behaviour of the CoP-CoG _v displacements over the short-term region. Analysis of the CoG _v displacements showed decreased RMS and increased MPF in the Biofeedback relative to the No-biofeedback condition. Stabilogram-diffusion analysis further indicated that these effects mainly stem from reduced spatio-temporal transition point co-ordinates at which the corrective process involving CoG _v displacements is initiated and an increased anti-persistent behaviour of the CoG _v displacements over the long-term region. Altogether, the present findings suggest that the main way the plantar pressure-based, tongue-placed tactile biofeedback improves postural control during quiet standing is via both a reduction of the correction thresholds and an increased efficiency of the corrective mechanism involving the CoG _v displacements.     

The agrin/muscle-specific kinase pathway: new targets for autoimmune and genetic disorders at the neuromuscular junction.

The increasing understanding of the structural complexity of the neuromuscular junction (NMJ), and the processes that are important in its development, suggests many possible new disease targets. Here, we summarize briefly the genetic and autoimmune disorders that affect neuromuscular transmission, and the identified targets, including new evidence that antibodies to muscle-specific receptor tyrosine kinase (MuSK) are involved in the pathogenesis of acetylcholine receptor (AChR) antibody-negative myasthenia gravis. We then review the development of the NMJ, focusing on the important roles of nerve-derived agrin and MuSK in clustering of AChRs and other essential components of the NMJ.